1. Field of the Invention
The present invention is directed to an x-ray diagnostics installation having an image intensifier video chain and means for detecting the average image brightness in a region of the image for controlling operation of the x-ray tube.
2. Description of the Prior Art
X-ray systems are known in the art wherein a selected portion, known as the dominant region, or simply the dominant, of the output image of the x-ray image intensifier is imaged onto a detector from which the average image brightness of that region is determined. The average image brightness can then be used for controlling operation of the x-ray tube to select the exposure time and to control the average image brightness in the region.
It is known to construct the detector of a matrix of photoelements, selected photoelements being activated in order to obtain a defined geometrical arrangement for forming an output signal, in accord with the desired dominant for brightness control and/or automatic deactivation of an x-ray exposure. Such a matrix, however, constitutes a relatively complicated and expensive structure.